Electric coupling system



M 15, 1938. c, TRUBE 211L483 ELECTRIC COUPLING SYSTEM Original Filed July 2, 1926 2 Sheets-Sheet 1 FREQUENCY o RESPONSE FREQUENCY FREQUENCY RESPONSE FREQUENCY RESPONSE.

INVENTOR I C E. Trube BY M QM ATTORNEYS E B U R T E C ELECTRIC COUPLING SYSTEM 2 Sheets-Sheet 2 Original Filed July 2, 1926 0 FREQUENCY INVENTOR Ca-r/ ETrube ATTORNEYS M nsa M 15,1938

snsc'mrc COUPLING SYSTEM Carl E. Trube, Maplewood, N. J., assignor to Hazeltine Corporation, Jersey City, N. L, a cor- 1 poration of Delaware Application July 2, 1926, Serial No.12o,o45 Renewed June 18. 1930 38. Claims.

'This'lnvention relates to electric coupling systems particularly adapted for use with radio-frequency vacuum tube amplifiers and more particularly to circuit arrangements which operate most effectively over a relatively wide range infrequency. This application is a continuation-inpart of my copending application Serial No. 101,- q

906, filed April 14, 1926. In United StatesLetters Patent No. 1,762,431, granted June 10, 1930, are shown electric coupling systems arranged to give effective operation over a range in frequency by providing a single manual device to adjust simultaneously the tuning and the voltage ratio. The present invention constitutes an improvement over that of the above-mentioned Patent No. 1,762,431 in that the coupling system is so arranged as to give a voltage ratio that varies automatically with the frequency thus leaving only the single adjustment of tuning for different frequencies. This simplifies the construction and increases the reliability of the system.

This invention is applicable both to coupling systems interposed between consecutive vacuum tubes of an amplifier, and to the coupling system interposed between an antenna and a vacuum tube. Furthermore, this invention is applicable to vacuum-tube amplifiers that are stabilized by the use of a high step-up voltage ratio in the coupling system, as described in my prior patent above referred to, to amplifiers that are stabilized by partial neutralization or by other means, and.

- to amplifiers wherein complete neutralization of capacity coupling is attained and wherein regenerationis eliminated.

The degree of responsiveness or amplification of an inter-tube coupling system is dependent, among other factors, on the voltage ratio of the system and the nature and magnitude of the input impedance of the system, which comprises the plate circuit load impedance of the preceding vacuum tube. Ordinarily, theinput impedance of such a system varies substantially over the tuning range of the system, following generally the impedance variations of the secondary tuned circuit, increasing with frequency when the secondary circuit is tuned bymeans of a variable condenser and decreasing with frequency when the secondary circuit is tuned by means of a variometer. As a result ofthis impedance variation, 50 at each frequency there is a particular ratio of output voltage to input voltage that will give the best compromise design. This ratio generally varies rapidly with the frequency, being relatively high at high frequencies. Similarly, in the antenna circuit, there is a voltage ratio that gives 1 in a desired manner.

the best compromise design, considering sensitivi-' ty and selectivity and this ratio also generally varies rapidly with frequency. This invention provides means for securing substantially the most desirable ratio at all frequencies in order to procure the most desirable frequency-response and selectivity characteristics without having any adjustable element except the tuning adjustment. Stated in another way, the present invention provides a new and improved means for procuring 10 an effective coupling between the input and output circuits of the coupling system that varies with frequency in a preselected manner under the control of the designer. By the term efiective coupling is meant the ratio of the effect coupled into the secondary or output circuit-which may be a current or a voltage, to the input or primary effect, which may also be either a current or a voltage. When the effective-coupling is measured as the ratio of the voltage coupled into the output circuit to the input current, asis the case 20 in an inter-tube coupling system, this ratio may be termed the efiective mutual reactance of the coupling system.

A feature of the invention is the maintenance, during tuning, of the effective reactance appearing at the output of the vacuum tube within such limits that the reaction upon the input circuit through the inherent interelectrode capacity of the tube is held within predetermined limits and in any event is insufficient to produce oscillations.

Referring to the drawings:

Fig. 1 illustrates a vacuum tube and an electric coupling system of the conventional type, in which the voltage ratio does not vary with the frequency. Fig. 1A is the response-frequency curve corresponding to Fig. 1.

Fig. 2 illustrates a modification of Fig. 1 and also is a conventional type. Fig. 2A gives respouse-frequency curves corresponding to Fig. 2 or to Fig. 6.

, Fig. 3 illustrates an electric coupling system in which the voltage ratio varies with the frequency in accordance with this invention, but in which the variation with frequency is more rapid than is usually desired. Fig. 3A is the corresponding response-frequency curve.

Fig. 4 illustrates a preferred form of this invention which combines Figs. 1 and 3 to give a voltage ratio which varies with the'frequency Fig. 4A is the responsefrequency curve corresponding to Fig. 4 or to Fig. .5.

Fig. 5 is the combination of Figs. 2 and 3 and gives results similar to those of Fig. 4.

Fig. 6 illustrates an alternative arrangement in vmich some of the advantages of this invention may be secured.

Fig. 7 also illustrates a modification of this invention in which some of the advantages may be secured. Fig. "7A is the corresponding response-frequency curve.

Fig. 8 is a further modification, in which the primary circuit is isolated from the secondary E1 measured at the input terminals of the cou-- pling system may be called the "accompanying alternating voltage or input alternating voltage. It may here be pointed out that the output voltage will in certain modifications of this invention be identical with the "resonant voltage, 1. e., the voltage across the adjustable .main resonant circuit, as in Figs. 3 and 6; while, in other modifications the output voltage will not necessarily be the same as the resonant voltage, as in Fig. 5.

In the coupling system of Fig. 1, the ratio of the output voltage E2 built up across the resonant circuit Ca, La to the accompanying alternating input voltage E1 across the coil L1 is substantially equal to the ratio of the self-inductance L2 to the mutual inductance M, and is therefore independent of the frequency. The rate at which the reactances and the resistances vary with the frequency, however, is such that the input impedance at resonance as measured between the terminals of L1 is relatively low at low frequencies. Therefore, both the effective coupling and the response or amplification are correspondingly low. For reasons of selectivity and stability, it is ordinarily the-practice to make the voltage ratio (Ea/E1) higher than that giving maximum amplification at the highest frequency. This is especially necessary in an unneutralized amplifier, where stability is particularly difilcult to attain at high frequencies. The result is that both the effective coupling and the amplification fall off markedly .at the lower frequencies, as illustrated by the full-line curve in Fig. 1A, which indicates qualitatively the relative response of a complete amplifier as a function of frequency. In a neutralized amplifier it is possible to lower the voltage ratio, by employing larger values of self-inductance L1 and thus of mutual inductance M, resulting in a response curve such as the dotted line in Fig. 1A; but still the amplification falls off at the lower end of the frequency range, and furthermore the selectivity is impaired at the higher frequencies. q

In place of the series-feed arrangement of Fig. 1, in which direct current is supplied by the battery 13 connected in series with the primary coil L1, it is sometimes the practice to employ a parallel-feed system as illustrated in Fig. 2, where the direct plate current is supplied through the choke coil L: which is eflectively in parallel with the input circuit of the coupling system, including condenser C5 and coil L1. It is the practice to design the choke coil 'L: and the blocking condenser Cs so that L3 offers a very high impedance to radio-frequency current, and

a,111,4sa

Cs a very low impedance; the former acting substantially as an open cirhuit and the latter as a short circuit. Under'these conditions, the system of Fig. 2 is electrically equivalent to that of Fig. l, and has therefore the same disadvantages, giving the same response-frequency curve, as representedby the full-line curve in Fig. 2A.

In the arrangements of the-,wprior art, of which Fig. 1 is typical, the coupling transformer generally has an effective step-up ratio greater than the optimum value; in other words, the primary or input impedance of the coupling system is less than the internal plate resistance of the tube. By virtue of the use of the greater than optimum value instead of the optimum value,v

the selectivity is greatly improved, while the amplification is decreased by only a small amount. In this region of operation, an increase in the efi'ective step-up ratio causes a further departure from the optimum value and results in decreasing the amplification, and vice versa.

In Fig. 3, there is provided a system essentially the same as that illustrated in Fig. 1 of my patent above referred to, but the condenser 0: now has a fixed capacity, and the condenser C4 alone is the adjustable tuning element. This circuit, like Fig. 2, embodies a parallel feed; and it will also be understood that the choke coil La has it very high impedance. The resonant circuit then includes the two condensers Ca and C4 and the inductance coil L2. As the impedance of La varies directly with the frequency, and the impedance of Ca varies inversely with the frequency, the ratio Ez/Ei of the resonant output voltage across L: to the accompanying alternating input voltage across Cs varies as the square of the frequency. Such a variation is in the right sense to result in an improvement over the constant ratio given by the arrangements of Figs. 1 and 2, and under some conditions may be satisfactory, particularly when stability is the most serious limitation and where the high-frequency losses in the coupling system are especially low, but ordinarily such a variation is too rapid in rate, resulting in a rapid falling off of both the effective coupling and the response at the higher frequencies, as shown in Fig. 3A.

In general, therefore, an effective combination of Fig. l or 2 with Fig. 3 will give the most desirable variation with frequency of the voltage ratio E2/E1 and of the response of the system. The combination of Fig. l with Fig. 3 is illustrated in Fig. 4, in which the main resonant circuit comprises the two condensers Ca and C4 and the inductance coil In. If, as before. L: is a choke-coil of very high impedance, then between the input terminals of the coupling system there are two coupling elements across which are developed two components of voltage: that across the electromagnetic or inductive coupling element L1 which is constant relative to the resonant output voltage E2; and that across the electrostatic or capacitive coupling element 03 which varies inversely as the, square of the frequency-relative to E2. Thus, there is obtained a resultant voltage ratio which increases with frequency but at a rate which is somewhat less than proportional to the square of the frequency, a variation of this sort being desirable ,for certain types of receivers. By properly choosing the magnitudes of the capacity C: and

voltage relative to the output voltage will fall oi! asthe frequencyincreases, but the. rate of falling oil. and thus the frequency-response character-- ,istic of the coupling system, isunder the control of the designer and the voltage ratio and responsecan begiven preselected values at any two specifled frequencies. Ordinarily, it is preferable to have the voltage across C3 considerably exceed that across L1 at the lower radio frequencies, while at the higher radio frequencies the voltage across L1 may be the greater. More specifically. elements Ca and L1 cause theratio of the output alternating voltage to the input voltage (Ea/E1) tofall off automatically when the tuning element is adjusted for higher frequencies, but at a'rate which is less rapid than the inverse square of the frequency. Under this condition, the response curve has a form such as illustrated in Fig. 4A.

In the coupling system of Fig. 4. coil L1 is ordinarily woundwith only a few turns, while coil L:

I is wound with many times that number. Capacity C3 is much larger than capacity C4. The actual inductance and capacity values may be of the same order of magnitude as the values given hereinafter for the identically numbered elements of the circuit of Fig. 5.

Fig. 5 illustrates the combination of Fig. 2 with that of Fig. 3, the coupling system, per se, being identical with that of Fig. 4 of my previously mentioned copending application, Serial No. 101,906. The operation is essentially the same as that just described for Fig. 4 and gives a responsefrequency curve as in Fig. 4A. The main resonant circuit in this instance comprises the two con densers Ca and C4 and the inductance coll L2. There is an advantage in the circuit arrangement of Figure 5 over the preceding circuits in that in the circuit of this figure the outputvoltage is the sum of the resonant voltage; (i. e., the voltage developed across the adjustable main resonant circuit C4, C3. L2) and the voltage across inductance L1. Ordinarily L3 is a choke-coil of very high impedance and C5 is a large capacity introduced to reinforce C3 and C4 in insulating for direct current; if L3 and C5 are made somewhat smaller they will have a qualitative effect in the radio-frequency system, but will not change the essential operation. The circuit of Fig. 5 was the basis of certain models of a successful commercial receiver known as the Thermiodyne.

In order that one skilled in the art may immediately practice this invention, the following constants for the system of Fig. 5 are given:

L1+L2=one tapped solenoid coil of 390 microhenries inductance, tapped so that L1=12 microhenries.

C5==lto milli-microfarads.

C3=2 to 10 milli-microfarads.

C4=variab1e condenser having a range of from to 220 micro-mlcrofarads.

La=a choke coil of not less than 500 microhenries inductance.

It will be observed that when values ofthe order of those given above as applicable to the system of Fig. 5 are assigned to the elements, the

auce of the tunable absorbing circuit is not reilected into the-said input circuit to a sufllcient extent to cause the output impedance connected to the amplifier to act'throughthe internal gridplate capacity of the saidiamplifier tube and cooperate with the currents in the amplifier input to a suflioient extent to produce oscillation. The tendency toward oscillations in amplifier coupling circuits is particularly pronounced when the input circuit of theampliiler tube is tunable in consonance with the tunable circuit associated with the coupling system inthe output of the amplifier tube; such tunable circuits are shown, for example, in Fig. 9.

The objects of this invention may be attained by a great number of circuits, of more or less complexity. For example, one of the simpler embodiments of the invention may comprise a modification of the circuit arrangement of Fig. 2 as by replacing the choke-coll In by a radio-frequency self-inductance and the blocking condenser C5 by a radio-frequency condenser, the two being designed to be resonant together at a frequency somewhat lower than the lowest frequency of the signals to be amplified. Under these conditions, the voltage ratio Ez/E1 is no longer substantially independent of the frequency, but falls off at the resonance of La and C5 in parallel, the increase in input impedance thus compensating at least in part for the variation in the coupling reactance provided by the coil L1. This arrangement, however, is not so desirable as that of Fig. 4 or Fig. 5; for the voltage ratio will be relatively too high at intermediate frequencies, with the result that the response curve tends to have a dip in the central portion, as illustrated by the dotted curve in Fi 2A. 7

In Fig. 6, which illustrates a coupling system in many respects similar to that system illustrated in Fig. 2 of my Patent No. 1,762,431 above referred to, the voltage ratio E2/E1 will be substantially constant if the coil L3 is a choke coil of high impedance. This voltage ratio is obtained from a double step-up, first between C3 and the combination of Ca and C5, and then between L1 and L2; but both of these step-up ratios are constant under the condition just stated. The response-frequency curve is then given by the full-line curve of Fig. 2A. However, if L3 is made a lower radio-frequency self inductance, so as to be resonant with the combination of C3 and C5 at a somewhat lower frequency than that of any signal to be amplified, then a variable voltage will be obtained which will automatically vary with the frequency in the same manner as for Fig. 2 when modified as described in the preceding paragraph. The response-frequency curve is then given by the dotted curve in Fig. 2A. The circuit of Fig. 6, when adjusted in this manner, was employed in some of the earlier models of the mentioned 'I'hermiodyne" receiver.

Fig. 7 shows a modification of Fig. 6, which obtains a voltage ratio which varies automatically with the frequency by the insertion of a small self-inductance L6 in series with C3. L6 is given such a value that its reactance is lower than that of condenser C3 at all frequencies to which the system is to respond. At relatively high frequencies it will subtract a relatively large portion of the reactance of C3, thus giving a relatively low voltage E1 between the plate and the filament. This makes the step-up ratio Ez/E1 increase as the frequency rises, which is the result desired.

except near the high-frequency end of the range. The result is that the voltage ratio is relatively too low at intermediate frequencies, and the response curve is corresponding y oo high, as illustrated in Fig. 7A. The system is therefore inierior to that of I"igs'.' 4 and 5.

Fig. 8 shows a system embodying my invention in which the primary circuit Cs, L1, In is isolated from the secondary circuit 0:, Le. The proportions of Co, Li and In and thecoupling's between L1, In and'Ic may be adjusted to give a desirable variation with frequency of the voltage ratio Es/Ei. This modification of my invention is more fully described in my United States Ietters Patent No. 1,763,380, granted June 10, 1930, which is a continuation-in-part of the present application. 1

Fig. 9 shows the application of the arrangement of Fig. 5 to a.. complete uni-control radio-frequency amplifier, both as coupling between the antenna and the grid of the first vacuum tube and as coupling between consecutive vacuum tubes. The advantages of applying such a compound coupling system to an antenna circuit are: first, to permit of attaining at all frequencies the most suitable compromise between sensitiv ity and selectivity; and second, to make the electrical constants of the tuned antenna system and the subsequent coupling systems substantially identical at all frequencies, so as to permit them to be tuned alike, particularly when it is desired to employ a single control for tuning all circuits, as has been done in the "'I'hermiodyne" receiver.

It is to be understood that by the'terms antenna and "antenna and ground", as employed in this specification and the appended claims, is meant any suitable system for collecting radiofrequency energy towhich the input terminals of an amplifier would customarily be connected.

I claim:

1. An electric coupling system adapted to be interposed between elements of a radio signaling apparatus, including terminals across which an alternating voltage is developed, a main resonant circuit across which an output voltage is developed, and means for adjusting said circuit over a certain frequency range, an input path through said coupling system, and means including said path for causing the ratio of the output voltage to the accompanying alternating voltage in said input path of the coupling system to rise as the frequency of said resonant circuit is increased, whereby high degrees of sensitivity, selectivity and stability are maintained.

2. A tuned radio-frequency coupling system interposed between elements of a vacuum tube radio-frequency amplifier, including terminals across which an alternating voltage is developed, an adjustable main resonant circuit across'which an output voltage is developed, an input path through said coupling system, and means including capacity and inductance in said input path for causing the ratio of the output voltage to the accompanying alternating voltage in said path to rise as the frequency is increased, whereby high degrees of sensitivity, selectivity and stability are maintained.

3. In a radio-frequency signaling apparatus including vacuum tubes, an electric coupling system including the combination of fixed reactive elements and a resonant circuit across which an output voltage is developed, said resonant circuit having a single adjustable tuning element, said coupling system being interposed between two vacuum tubes of ssid apparatus, said fixed reactive elements being so arranged that between two points thereof there is developed an alternating voltage which automatically falls all relative to said output voltage when said tuning element alone is adjusted for higher frequencies.

4. In a radio-frequency vacuum tube amplifier, an electric coupling system including a combination of fixed reactive elements and a resonant circuit across which an output voltage is developed, said resonant circuit having a single ad- Justable tuning element, said coupling system being interposed between two vacuum tubes oi. said amplifier, each tube having a grid, aplate and a filament, said output voltage being impressed across the grid and the filament of one of said vacuum tubes, said fixed reactive elements being so related to each other and to said vacuum tubes that between the plate and the filament of the other of said tubes there is developed an alternating voltage which automatically falls of! relative to said output voltage when said tuning element alone is adjusted for higher frequencies.

5. In a radio amplifier stage, including a vacuum tube having a filament, a grid and a plate, an electric coupling system comprising a main resonant circuit in which a resonant voltage is built up, a path through said coupling system between said plate and said filament, a fixed condenser in series both with said path and with said main resonant circuit, and reactive means so associated with said path and with said main resonant circuit that there is developed in said path a voltage whose ratio to said resonant voltage falls rapidly as the frequency is increased.

6. A system of amplification of radiant energy comprising an electronic device, a transformer, a tuning capacity, a capacity connected in series between the primary and secondary of the transformer, said capacity being also in series with the tuning capacity, and both capacities being connected in shunt across the secondary of the transformer, and the electrical values of the said inductances 'of the transformer and of the said capacities being relatively such that the system is essentially nonregenerative.

7. A system of amplification of radiant energy as set forth in claim 6 which provides capacities to form an electrostatic path of energy transfer whose value' is definitely variable, and inductances comprising a transformer to form an electromagnetic path whose value is naturally variable with changes of frequency; the electrical relationship of these two paths and their values being such'that a maximum transfer of energy is obtained without regeneration or any fiow of undesirable disturbing currents at any desired frequency. a

8. A system of amplification of radiant energy as set forth in claim 6 which comprises an electromagnetic and an electrostatic path of energy transfer whose values are variable, automatically, by the act of tuning, said values being so related to each other as to produce a zero difi'erence of potential in respect to all undesired currents between the grid and plate of the electronic device when the set is tuned to any given frequency.

9. A system of amplification of radiant energy comprising an electronic device, a transformer, a tuning capacity, a capacity connected in series between the primary and secondary of said transformer, said capacity being also in series with the tuning capacity and both capacities being connected in shunt across the secondary of the transformer, and the electrical values of said inductancesand capacities being so selected and so related to each other as tosimultaneously comprising an electronic device having an output circuit which comprises a transformer, a variable condenser, and a series condenser, said variable and series cor'idensers being connected in series with each other and the two being connected in shunt across the secondary of said transformer and one end of the primary of said .transformer being connected into the series connection between the two said condensers and their values being selected so as to prevent the production of undesired disturbing oscillations in the electronic device.

11. In a system of amplification of radiant energy comprising an electronic device, a transformer, a tuning capacity, a capacity connected in series between the primary and secondary of said transformer, said'capacity being also in series with the tuning capacity, and both capacities being connected in shunt across the secondary of the transformer, the process'of simultaneously maintaining a condition of complete non-regeneration and a condition of energy transfer maintained constant at its maximum value over any desired range of frequency by the selection and. relation of the electrical values of said inductances and capacities.

12. An electric coupling system for coupling a pair of input terminals to a pair of output termi nals, said system comprising an inductive coupling element which acting alone would produce a voltage across said output terminals which rises with increasing frequency, and reactance means included in said system for maintaining said out put voltage fairly constant over a substantial range of frequency.

13. An electric coupling system for interposition between a pair of input terminals and a pair of output terminals, said system comprising an exciting circuit and a tunable output circuit coupled to said exciting circuit, said exciting circuit including an element which acting alone would produce a voltage in said output circuit which rises with increasing frequency, and reactive means in said exciting circuit for causing the voltage across said input terminals to decrease with increasing frequency, whereby the voltage across said output terminals remains substantially constant.

14. An electric coupling system having a pair of input terminals and a pair of output terminals,

- said system comprising an exciting circuit connected to said input terminals and an absorbing circuit connected to said output terminals and coupled to said exciting circuit, said system including only one manually variable element which selects the frequencies transmitted by said system, and said exciting circuit including elements whose impedances vary with frequency in such a manner that the voltage across said input terminals automatically decreases when the tuning frequency is increased, while the output voltage remains substantially constant.

15. An electric coupling system comprising two pairs of terminals, a variable condenser-tuned circuit connected with one of said pairs of terminals and a network including fixed reactance elements connected with the other of saidpairs of terminals, at least one of said elements being coupled to said tuned circuit, and at least two of said elements having diflerent reactance variations with change of frequency, whereby the total effective coupling can be made any desired function of the frequency to which said circuit is tuned.

16. A tuned radio-frequency coupling system comprising two pairs of terminals, a tunable circuit connected with one ofsaid pairs of terminals,

' and a network including fixed reactance elements connected with the other of said pairs of terminals, at least one of said elements being coupled to said tunable circuit, and at least two of said elements having different reactance variations with change of frequency, the values of said two elements being so proportioned and said elements being so related to said tunable circuit that the total effective coupling is a preselected-function of the frequency to which said circuit is tuned.

17. A tuned radio-frequency coupling system comprising two pairs of terminals, a tunable circuit connected with one of said pairs of terminals and a network of fixed reactance elements connected with the other of said pairs of terminals, at least one of said elements being inductively coupled to said tunable circuit, and at least two of said elements having opposite reactance variations with frequency, whereby the effective mutual'reactance can be made substantially independent of the frequency to which said circuit is tuned.

18. A tuned radio-frequency coupling system comprising two pairs of terminals, a tunable circuit including a variable condenser and a fixed inductance connected in parallel to one of said pairs of terminals and a network of fixed reactance elements connected with the other of said pairs of terminals, at least one of said elements being coupled to said tuned circuit, and at least two of said elements having different reactance variations with frequency, the values of said two elements being so proportioned and said elements being so related to said tunable circuit that the total effective coupling is a preselected function of the frequency to which said circuit is tuned.

19. A radio-frequency coupling system comprising two pairs of terminals, a tunable circuit including a variable condenser and a fixed inductance connected in parallel to one of said pairs of terminals, and a network of fixed reactance elements connected with the other of said pairs of terminals, at least one of said elements being capacitively coupled to said tunable circuit, and at least two of said elements having opposite reactance variations with frequency, the values of said two elements being so proportioned and said elements being so related to said tunable circuit that the total effective coupling is a preselected function of the frequency to which said circuit is tuned.

20. A tuned radio-frequency coupling system comprising two pairs of terminals, a tunable circuit connected with one of said pairs of terminals, and a network including fixed reactance elements connected with the other of said pairs of terminals, at least one of said elements being coupled to said tunable circuit, and at least two of said elements having different reactance variations with change of frequency, said fixed reactance elements being of such types and having such circuit relationship with each other and with said tunable circuit that the total effective coupling can be made any desired function of the frequency to which said circuit is tuned by properly proportioning the values of said elements.

21. A tuned radio-frequency coupling system comprising two pairs of terminals, a tunable circuit connected with one of said pairs of terminais, and a reactance network connected to the other of said pairs of terminals andincluding fixed reactance means coupled to said tunable circuit which acting alone produces a ratio ofv output voltage to input current which varies in a predetermined manner with the frequency to which said circuit is tuned and fixed reactance means for substantially modifying the manner of variation of the voltage introduced into said tunable circuit by said input current as said circuit is tuned over its range, thereby to modify said ratio of output voltage to input current in a preselected manner.

22. A tuned radio-frequency coupli system comprising two pairs of terminals, a tunable circult connected with one of said pairs of terminals, and a reactance network connected to the other of said pairs of terminals and including fixed reactance means coupled to said tunable circuit which acting alone produces a ratio of output voltage to input current which increases with the frequency to which said circuit is tuned, and means for varying the voltage introduced into said tunable circuit by said input current inversely in accordance with said frequency to' which said circuit is tuned, thereby to compensate at least in part for the variations in said ratio.

23. An electrical system composed of an amplifier of alternating currents, a tunable input circuit, an output circuit, an internal path in said amplifier connecting said output circuit to said input circuit, a tunable absorbing circuit associated with said output circuit, and nieans for limiting amplified energy feedbaclg through said internal path comprising means for loosely coupling said absorbing circuit to said output circuit and electrical elements maintaining said coupling constant while said absorbing circuit is tuned in consonance with said input circuit.

24. An electrical amplifying system including a three-electrode vacuum tube, an adjustable period circuit connected to the input electrodes of said tube, an output circuit, a responsive device,

and means for controlling the reaction of said output circuit and abstraction of energy therefrom for said responsive device over a wide range of frequencies that a predetermined effect in said responsive device with frequency is obtained, in-

ciuding a circuit coupled to said output circuit adapted to be adjusted in period in consonance with said adjustable period input circuit, and across which second adjustable circuit said responsive device is connected, said coupling including a pair of coupling elements transferring energy in phase, one of which couplings increases in effect with frequency increase and the other of which couplings decreases in effect with fre-. quency increase, the relative values of said couplings being chosen to give the said predetermined eifect over a wide range of frequencies.

25. In an electrical system including a source of alternating currents of a wide range of frequencies, the electrical conduct of said source towards currents of diflerent frequencies depending upon the nature of the reactions to said currents of different frequencies of a circuit connected to the output terminals thereof, the method of controlling said reactions with frequency as the current output of said source is changed from frequency to frequency which consists of selectively absorbing energy both elcctl'ostatically and electromagnetically in phase from said output circuit in frequency consonance with the currents therein to selectively create absorption reaction thereon, controlling said selective absorption elec-' trostaticaliy whereby said electromagnetic absorption decreases with frequency decrease, and so relating the'variation of electrostatic absorption to the necessary electrostatic variation for selectiveabsorption that said electrostatic ab sorption increases with frequency decrease at such rate that the effect of said electromagnetic absorption on the reactions of said output circuit with frequency is modified in a desired way.

26. In an electrical system including a source of alternating currents'of a wide range of frequencies, the electrical conduct of said source towards currents of different frequencies depending upon the nature of the reactions to said currents of difierentfrequencies of a circuit connected to the output terminals thereof, the method of controlling said reactions with frequency as the current output of said source is changed from frequency to frequency which consists of selectively absorbing energy fromsaid output circuit by way of a coupling which transfers 27. In an electrical system the combination of a source of alternating currents of a wide range of frequencies, an output circuit, the electrical conduct of said source towards currents of different frequencies depending upon the natureof the reactions of said output circuit to said currents, and means for controlling the electrical conduct of said source from frequency to frequency through control of said reactions comprising a circuit variable in period over said wide range-of frequencies coupled to said output circuit through a coupling which changes the ab-' sorption reaction of said variable circuit on said output circuit as varied from frequency to frequency, and a second coupling between said circuits in phase accord with said first coupling, said second coupling being adapted to change the absorption reaction of said variable circuit'on said output circuit from frequency to frequency inversely to the change produced by said first coupling.

28. The method of transferring electrical energy throughout a range of frequencies from an exciting circuit to a tunable absorbing circuit, which consists of transferring the energy both electromagnetically and electrostatically in aiding phase, and causing said electrostatic energy transfer to decrease as said absorbing circuit is tuned in such sense as to increase the frequency of the energy so selected'for transfer in substantially the same degree as the electromagnetic energy transfer increases through such tuning.

29. An electrical energy transfer system comprising means for transferring energy throughout a range of frequencies from anexciting circuit to a tunable absorbing circuit including a coupling between said circuits comprising in combination amass ing an exciting circuit and a tunable absorbing circuit, an electrostatic coupling between said circuits, and an electromagnetic coupling betweensaid circuits, said couplings being so poled and relatively adjusted that, for such adjust-Q ment, their combined energy transfer remains substantially constant with'frequency as said absorbing circuit is variably tuned.

. 31. The method of transferring electrical energy throughout a range of frequencies from an exciting circuit to a tunable absorbing circuit,f

which consists of transferring the energy both electromagnetically and electrostatically in aiding phase, and causing said electrostatic transfer to vary in a preselected manner as said absorbing circuit is tuned.

32. The method of transferring electrical energy throughout a range of frequencies from an exciting circuit to an absorbing circuit whose constants include a capacitive reactance divided into two portions, which consists of transferring energy in aiding phase both electromagnetically and, through one of said capacitive portions, ad-

justing'said absorbing circuit for resonance with desired current frequencies in said exciting circuit by varying the other of said capacitive portions, and adjusting the relative values of said capacitive portions to produce an energy trans-.

fer that combines with the electromagnetic energy transfer to produce a combined transfer that varies in a preselected manner with frequency.

33. An electrical energy transfer system in-- said circuits adapted to decrease in a preselected manner with increase of frequency as said .absorbing circuit is tuned, an electromagnetic coupling between said circuits so poled as to transfer energy in phase with said electrostatic coupling,

comprising a circuit tunable over a wide range of radio frequencies,'another circuit to be coupled therewith, fixed reactance coupling means ineluding inductance for providing coupling therebetween; which varies with frequency in one sense as said tunable circuit-is tuned over said range,

and fixed reactance coupling means including capacitance for providing coupling therebetween which varies with frequency in the opposite sense, said coupling means beingrelatively poled in aiding phase, whereby the coupling variation of one said means at least partially compensates -for the coupling variation of the other said means.

36. A tunable radio-frequency coupling system comprising a resonant circuit including inductive and capacitive elements, only one of said elements being adjustable for tuning ,said circuit over a wide range of radio frequencies, an-

other circuit to be coupled therewith, fixed reactance coupling means including inductance for providing coupling therebetween which varies with frequency in one sense as said tunable circuit is tuned i'over said range, and fixed reactance coupling means including capacitance for providing coupling therebetween which varies with frequency in the opposite sense, said coupling means being relatively poled in aiding phase, whereby the coupling variation of one said means at least partially compensates for the over a wide range of radio frequencies, another circuit to be coupled therewith, fixed reactance coupling means including inductance for providing couplifig therebetween which increases with increasing frequency as said tunablecircuit is tuned over said range, and fixed reactance coupling means including capacitance for providing coupling therebetween which decreases with increasing frequency, said means being relatively poled in aiding phase, whereby the coupling variation of one said means at least partially compensates for the coupling variation of the other said means.

'38. A tunable radio-frequency coupling system comprising a resonant circuit including in series a fixed inductance element, a fixed capacitance element and an adjustable capacitance element for tuning the circuit over a wide range of radio frequencies, and another circuit including in series said fixed capacitance element and another fixed inductance element inductively cou- -'pled with that of said resonant circuit, said inductive coupling being poled to aid the coupling of said fixed capacitance, whereby the variation of coupling due to. said fixed capacitance element at leastpartialiy compensates for the cou- OARLETR'QBE.

.pling variation due to said inductive coupling as said resonant circuit is tuned over said range. so 

